Anyone who has ever been to school would have seen many blackboards big and small on which characters in different colors of chalk are written. The blackboard is a kind of cutural tool. It is usually made of wooden boards four to five eenlimeters thick in the shape of a rectangle. It is painted black on the surface with black pednt. Underneath there is a groove for dust. With the development of the educationaI cause， there has been an increasing development in cultural facilities and equipment. The varicty of blaekboards is on the rise. There are glass-made blackboards， velvet blackboards made on the basis of the function of statics， magnetic black-boards made according to the function of magnetics， etc.
    The blaekboard is so common and unattractive in our life， yet it has played an important role in our study， Our teachers have written equation after equation and solved countless problems on it. It is such a common rectangular blackboard， but it is the golden key to the door of the treasure house of knowledge.
    黑板
    任何到過(guò)學(xué)校的人，總見(jiàn)過(guò)許多大大小小的，上面寫(xiě)著各種顏色粉筆字的黑板。黑板是一種常見(jiàn)的文化工具，它一般呈矩形，用本質(zhì)夾板做成，厚四五厘米。它的正面涂上黑漆，下面還有一條積灰槽。
    教育事業(yè)的發(fā)展，促進(jìn)了文化用品的發(fā)展。黑板的品種不斷增多，有玻璃黑板，有根據(jù)靜電作用造出的絨布黑板，有根據(jù)磁性作用造成的磁性黑板……
    黑板在生活中是司空見(jiàn)慣的，然而卻在我們的學(xué)習(xí)中起著重要作用。老師在黑板上寫(xiě)下一個(gè)又一個(gè)的方程，解決了無(wú)數(shù)難題。就這樣一個(gè)普通的長(zhǎng)方形黑板，可卻是通往知識(shí)寶庫(kù)的金鑰匙。